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We characterize and provide a catalog of thirty >100 MeV sustained gamma-rayemission (SGRE) events observed by Fermi LAT. These events are temporally andspectrally distinct from the associated solar flares. Their spectra areconsistent with decay of pions produced by >300 MeV protons and are notconsistent with electron bremsstrahlung. SGRE start times range from CME onsetto two hours later. Their durations range from about four minutes to twentyhours and appear to be correlated with durations of >100 MeV SEP proton events.The >300 MeV protons producing SGRE have spectra that can be fit with powerlaws with a mean index of ~4 and RMS spread of 1.8. Gamma-ray line measurementsindicate that SGRE proton spectra are steeper above 300 MeV than they are below300 MeV. The number of SGRE protons >500 MeV is on average about ten times morethan then the number in the associated flare and about fifty to one hundredtimes less than the number in the accompanying SEP. SGRE can extend tens ofdegrees from the are site. Sustained bremsstrahlung from MeV electrons wasobserved in one SGRE event. Flare >100 keV X-ray emission appears to beassociated with SGRE and with intense SEPs. From this observation, we providearguments that lead us to propose that sub-MeV to MeV protons escaping from theflare contribute to the seed population that is accelerated by shocks onto openfield lines to produce SEPs and onto field lines returning to the Sun toproduce SGRE.

Characteristics of Sustained >100 MeV Gamma-ray Emission Associated with Solar Flares